Patent Application
20050061473
The invention relates to heat exchangers. The invention has broad application to heat exchangers used to deliver heat to or remove heat from objects as diverse as electrical or electronic devices or equipment, mechanical devices such as transmissions, spindles, compressors and engines, scientific and medical apparatus, living creatures, and the like.
There are numerous situations where it is desirable to remove heat from an object or to deliver heat to an object. Various types of heat exchanger exist. Air cooled heat sinks are structures which take heat from an object and dissipate the heat into ambient air. Such heat sinks typically consist of a finned piece of thermally conductive material having a face which can be placed in thermal contact with an object, such as an electronic component, to be cooled. Some heat sinks are equipped with fans located to flow air past the fins to improve the rate at which heat is dissipated.
U.S. Pat. No. 6,549,411 B1 discloses a flexible heat sink that can be attached to a generally flat surface of an object. The heat sink can flex to conform to the surface of the object to achieve improved contact with the object, and hence increase the efficiency of heat transfer between the heat sink and the object. U.S. Pat. No. 6,367,541 B2 discloses a heat sink that can be attached to multiple electronic chips which have different heights. The heat sink dissipates heat from the chips into ambient air.
U.S. Pat. No. 5,368,093 discloses a flexible bag filled with thermal transfer fluid useful for thawing frozen foods. U.S. Pat. No. 4,910,978 discloses a flexible pack containing a gel. The pack can be cooled and applied to a patient for cold therapy. The pack conforms to surface contours of the patient's body. These devices have limited cooling capacities.
More sophisticated heat exchangers use a heat exchange fluid, typically a liquid, instead of ambient air to carry heat away from or provide heat to an object to be cooled or heated. U.S. Pat. No. 5,757,615 discloses a flexible heat exchanger with circulating water as a coolant for cooling a notebook computer. U.S. Pat. No. 5,643,336 discloses a flexible heating or cooling pad with circulating fluid for therapeutically treating the orbital, frontal, nasal and peri-oral regions of a patient's head. U.S. Pat. No. 6,551,347 B 1 discloses a flexible heat exchange structure having fluid-conducting channels formed between two layers of flexible material for heat/cold and pressure therapy. U.S. Pat. Nos. 6,197,045 B1 and 6,375,674 B1 disclose a flexible medical pad with an adhesive surface for adhering the pad to the skin of a patient. U.S. Pat. No. 6,030,412 discloses a flexible enveloping member for enveloping a head, neck, and upper back of a mammal for cooling the brain of the mammal suffering a brain injury. All of these heat exchangers require heat to pass through a layer of some flexible material such as rubber, or a flexible plastic such as polyurethane. In addition, heat is exchanged between the surface of the flexible material and a circulating fluid. Water is the most commonly used circulating fluid.
Rubber and flexible plastics are poor conductors of heat. To provide a high heat transfer efficiency in a flexible heat exchanger in which heat is transferred across a layer of rubber or plastic the layer must be very thin. This makes such heat exchangers prone to damage. In addition, water is a poor heat conductor. Heat exchange between the flexible material and water is largely dependent on convection. Water flowing over a relatively flat surface will not result in efficient heat exchange.
U.S. Pat. No. 3,825,063 discloses a heat exchanger having metal screens of fine mesh with internal plastic barriers that at least partly penetrate the screens. The screens are stacked to provide transverse heat conduction relative to longitudinal flow paths. U.S. Pat. No. 4,403,653 discloses a heat transfer panel comprising a woven wire mesh core embedded in a layer of plastic material. The mesh and closure layer extend in the same longitudinal direction. U.S. Pat. No. 5,660,917 discloses a sheet with electrically insulating thermal conductors embedded in it. The apparatus disclosed in those patents is not adapted for warming or cooling living subjects.
There remains a need for heat exchangers capable of providing high heat transfer rates between the heat exchangers and objects that are not flat, are vibrating or are otherwise difficult to interface to. There is a particular need for such heat exchangers which have high ratio of heat-transfer capacity to contact area.
The invention relates to heat exchangers. One aspect of the invention provides flexible heat exchange interfaces. The interfaces have plates of elastomeric material penetrated by substantially rigid thermally conductive members. The thermally conductive members have enlarged pads on at least one side of the plate.
The elastomeric material allows the interfaces to flex while the thermally conductive members are operative to channel heat from a higher-temperature side of the interface to a lower-temperature side of the interface.
Another aspect of the invention provides a flexible heat exchanger comprising a volume having an inlet and an outlet. The volume can receive a heat exchange fluid, for example, water or a water-based coolant. The heat exchanger includes a flexible plate. Substantially rigid thermally conductive members extend through a flexible material of the flexible plate from an outside surface of the flexible plate into the volume.
In preferred embodiments the thermally conductive members each have a thermal conductivity of at least 50 Wm−1K−1 and preferably at least 100 Wm−1K−1. The thermally conductive elements may be made of materials such as aluminum, copper, gold, silver, alloys of two or more of aluminum, copper, gold, or silver with one another, alloys of one or more of aluminum, copper, gold, or silver with one or more other metals, carbon, graphite, diamond, or sapphire.
The thermally conductive members may cover a substantial portion of the outer surface of the flexible heat exchange plate. For example, the thermally conductive members may be exposed in an area of at least 50%, preferably at least 70% and, in some embodiments, at least 80% of an area of the flexible heat exchange plate.
The flexible material of the plate may comprise an elastomer material. The thermally conductive members may be embedded in the elastomer material by any suitable process. The elastomer material may comprise, for example, natural rubber, polyurethane, polypropylene, polyethylene, ethylene-vinyl acetate, polyvinyl chloride, silicone, or a combination of two or more of polyurethane, polypropylene, polyethylene, ethylene-vinyl acetate, polyvinyl chloride, and silicone. In some embodiments the elastomer material has a thermal conductivity not exceeding 5 Wm−1K−1.
A further aspect of the invention provides a temperature control system comprising a heat exchanger according to the invention, a reservoir containing a heat exchange fluid; a first feed pump connected to feed heat exchange fluid from the reservoir into the heat exchanger and a second feed pump connected to withdraw the heat exchange fluid from the reservoir.
Further aspects of the invention and features of specific embodiments of the invention are described below.
In drawings which illustrate non-limiting embodiments of the invention:
Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.
Heat exchangers according to the invention have thermally conductive members which can be placed in thermal contact with an object to be heated or cooled. The thermally conductive members pass through a membrane of a flexible material. In some embodiments the membrane is essentially impermeable to a heat exchange fluid that contacts portions of the thermally conductive members that are distal to the object. The membrane permits the heat exchange members to move relative to one another to conform with surface contours of the object. For example, the membrane may permit the members to conform to a convex and/or concave curved surface on the object.
The thermally conductive members accept heat from a higher-temperature side of the membrane, channel the heat through the membrane, and release the heat to a lower-temperature side of the membrane. The members provide much lower thermal resistance than would be the case if the members were not present.
In some embodiments, the members have pads on their ends proximate to the object. The pads are dimensioned and distributed in such a manner that the pads cover a large proportion of a heat exchange area of the membrane. In certain embodiments of the invention, pads of a plurality of the thermally conductive members cover at least 50%, preferably at least 70%, and most preferably at least 80% of an area of the outer side of the membrane.
An inner side of the membrane may define one side of a channel which carries a heat exchange fluid. Heat exchange fluid may be driven to flow through the channel by way of a suitable pumping system to deliver heat to, or draw heat from, the thermally conductive members.
In some embodiments of the invention a plurality of the thermally conductive members have thermally conductive projections, which may comprise, for example, pins, fins, bars, plates or the like that project into the volume of a heat exchanger to form an efficient heat exchange interface with heat exchange fluid in the volume. The projecting pins, fins, bars, plates or the like may or may not be similar in shape or other physical characteristics to the parts of the thermally conductive members that extend through the membrane to form thermal channels through the membrane.
The thermally conductive members may be made of any suitable thermally conductive materials including thermally conductive metals, for example, aluminum, copper, gold, silver, or alloys of these metals with one another and/or with other metals. The thermally conductive members may also be made of non-metals which have high thermal conductivities such as carbon, suitable grades of graphite, diamond, sapphire or the like. Preferably the thermally conductive members are made from materials having thermal conductivities, k, of at least 50 Wm−1K−1 and preferably at least 100 Wm−1K−1.
Thermally conductive members 14 pass through the material 30 of plate 12. Inside ends 26 of thermally conductive members 14 project into volume 20. Ends 26 preferably project significantly into volume 20. In the embodiment shown in
In some embodiments, pads 29 have thicknesses in the range of 0.5 mm to 5 mm. Preferably, pads 29 have thicknesses in the range of 1 mm to 2.5 mm. The sizes and dimensions of pads 29 in the plane of plate 12 may be chosen to suit the application, taking into consideration the contours of the object to be cooled or heated.
Thermally conductive members 14 may have reduced cross sectional areas in their portions toward inner face 18 from pads 29. The cross-sectional area of thermally conductive members 14 at the point that thermally conductive members 14 emerge from material 30 on inner face 18 of plate 12 may, for example, be in the range of 20% to 100%, and in some embodiments is 35% to 65%, of the area of pads 29.
Thermally conductive members 14 have lengths sufficient to pass through material 30. In preferred embodiments, members 14 project into volume 20. Thermally conductive members 14 may, for example, project into volume 20 for a distance in the range of 0 mm to 100 mm. For small heat exchangers the projection may be at the lower end of this range (i.e. in the range of 0 mm to 20 mm). The portions of members 14 which project into volume 20 may also function as supports to maintain a minimum spacing between wall 24 and plate 12. These portions may constitute spacing means for preventing rear wall 24 from collapsing against plate 12.
It is not necessary that all thermally conductive members 14 be identical or that all thermally conductive members 14 have equal-sized pads 29 although it is convenient to make heat exchanger 10 with thermally conductive members 14 substantially the same as one another.
Material 30 constitutes a flexible membrane through which thermally conductive members 14 extend. In some embodiments, rear wall 24 is made of material 30. Substantially all of heat exchanger 10, except for thermally conductive members 14, may be made of the same material 30. Material 30 is preferably both flexible and elastically stretchable. Material 30 may, for example, comprise natural rubber or any of a variety of suitable flexible polymers such as polyurethane, polypropylene, polyethylene, ethylene-vinyl acetate, polyvinyl chloride, silicone, a combination of these materials or the like. Material 30, or portions of material 30 may optionally be loaded with particles of one or more thermally conductive materials such as metal or graphite. However, since material 30 is not required to play a significant role in conducting heat, material 30 may be a material having a relatively low thermal conductivity (i.e. a thermal conductivity not exceeding 5 Wm−1K−1) without significantly impairing the function of heat exchanger 10. In some embodiments, material 30 has a hardness in the range of 10 to 80 on the Shore A hardness scale.
Plate 12 may be fabricated using any suitable process. For example, plate 12 may be made by making holes in a sheet of material 30 and inserting thermally conductive members 14 through the holes. The holes may initially have dimensions smaller than corresponding dimensions of thermally conductive members 14 so that material 30 seals around thermally conductive members 14 sufficiently to prevent any significant loss of heat exchange fluid from volume 20. Additionally, or in the alternative, a sealant, such as a suitable glue, may be provided to enhance the seal between thermally conductive members 14 and material 30. Plate 12 may also be made by a suitable plastic manufacturing process such as thermal injection molding, reaction injection molding, compression molding, vacuum forming or casting. In this case, thermally conductive members 14 may be molded into plate 12.
The thickness of material 30 in plate 12 can be selected to provide a desired compromise between flexibility and durability. Since heat exchanger 10 does not rely on material 30 to conduct heat, it is not necessary to make material 30 extremely thin to improve heat conduction. Material 30 may, for example, have a thickness in the range of about 1 mm to 20 mm. In some currently preferred embodiments of the invention, material 30 has a thickness in the range of 3 mm to 7 mm in plate 12.
Projections of material 30, or some other material, may optionally extend into volume 20. Such projections may be positioned to support wall 24 relative to plate 12, to direct the flow of fluid 65 within volume 20 and/or to induce turbulence at selected locations in the flow of fluid 65 in order to provide enhanced thermal contact between thermally conductive members 14 and heat exchange fluid 65. Such projections may constitute spacing means for preventing rear wall 24 from collapsing against plate 12.
Thermally conductive members 14 may be arranged in a wide range of patterns. For example, as shown in
Flexing of plate 12 may be facilitated by arranging members 14 to provide substantially unbroken lines 31 of material 30 extending generally parallel to one or more axes about which heat exchanger 10 may be flexed. The embodiment shown in
Thermally conductive members 14 may take any of a wide variety of forms which provide effective means to transfer heat from a higher-temperature side to a lower-temperature side of the membrane. The members preferably provide good thermal interface between the thermally conductive members and the object to be cooled or heated, good thermal channels across membrane material 30, and good thermal interface between the thermally conductive members and the heat exchange fluid in volume 20 of the thermal exchanger.
Some possible forms for members 14 are illustrated in
Heat exchangers according to the invention may be pre-formed so that surface 16 has a concave and/or convex curvature in the absence of applied forces.
Heat exchangers according to the invention may be applied to heating or cooling objects of diverse types. For example,
Heat exchangers according to the invention may also be used to transfer heat between fluids and/or between solid objects.
A suitable circulation system may be used to circulate a heat exchange fluid through the volume 20 of one or more heat exchangers as described herein. Water has a high specific heat capacity which makes water or water-based coolants good for use as a circulating fluid 65 in cases where fluid 65 can operate at temperatures where such coolants are liquid.
It is generally desirable to maintain the pressure of fluid in volume 20 approximately equal to the ambient air pressure surrounding heat exchanger 10. If the pressure within volume 20 is significantly smaller than the ambient air pressure then pressure differences across the walls of volume 20 will tend to collapse volume 20. The projected ends 26 of thermally conductive members 14 or other supports provided in heat exchanger 10 may prevent the walls from complete collapse. If the pressure within volume 20 is significantly larger than the ambient air pressure then heat exchanger 10 will tend to balloon.
A first feed pump 70 upstream from heat exchanger 10 delivers fluid 65 from reservoir 64 to heat exchanger 10. A second feed pump 72 is located downstream from heat exchanger 10. Second feed pump 72 draws fluid 65 from heat exchanger 10 and returns the fluid to reservoir 64. First and second feed pumps 70 and 72 are balanced so that the pressure of fluid 65 within volume 20 of heat exchanger 10 is substantially equal to the ambient air pressure.
One or more bypass valves may be provided to provide better control over fluid pressure within volume 20. In system 100, an adjustable bypass valve 74 is connected between the output of first feed pump 70 and reservoir 64. Bypass valve 74 indirectly regulates the pressure within volume 20. When bypass valve 74 is opened, a larger proportion of fluid 65 is returned to reservoir 64 by way of bypass conduit 75 and the amount of fluid 65 flowing into heat exchanger 10 is reduced. Bypass valve 74 may be pressure-operated.
System 100 has a second bypass valve 76 connected in parallel with second feed pump 72. When second bypass valve 76 is open, second feed pump 72 can draw fluid 65 from reservoir 64 by way of conduit 77. Opening second bypass valve 76 increases pressure at the input of second feed pump 72 and consequently increases the pressure within volume 20.
Many variations of system 100 are possible. Although two bypass valves are shown in
In some cases it may be convenient to provide a single reservoir 64 for providing heat exchange fluid for multiple heat exchangers 10. In such cases it is best to provide upstream and downstream pumps 70 and 72 for each heat exchanger 10. In the alternative, suitable manifolds, such as T-connectors, could be provided to allow a number of heat exchangers 10 to be connected in parallel between a single upstream pump system and a single downstream pump system.
System 61A has a second flow regulator 79 which includes a second flow restrictor 84 and a bypass valve 86. Bypass valve 86 is connected in parallel with restrictor 84. In system 100A, bypass valves 82 and 86 are adjustable. The fluid pressure within volume 20 can be controlled by adjusting one or both of bypass valves 82 and 86.
Some alternative embodiments of the invention lack one of flow regulators 78 and 79. When system 100A is connected to supply fluid 65 to a plurality of heat exchangers 10 it is preferable to provide for each heat exchanger 10 at least one adjustable flow regulator 78 or 79 located where only fluid going to or from that heat exchanger passes through the flow regulator. This permits the pressure within each heat exchanger 10 to be individually regulated. In the alternative, as described above, suitable manifolds may be provided to split the flow of fluid 65 between a number of heat exchangers 10 connected in parallel.
In the illustrated embodiment, control is accomplished by operating a power splitter 88 (illustrated schematically by a potentiometer). Power splitter 88 can be operated to increase the speed of a motor driving pump 70 and to decrease the speed of a motor driving pump 72 or vice versa.
Systems 100, 100A and 100B may be automatically controlled using any suitable control system. For example, a controller may be provided to operate bypass valves and/or control pump speeds or displacements by way of suitable actuators (not shown) as necessary to control pressure within volume 20 to stay within a desired range. Those skilled in the art are familiar with suitable controllers. The controller may, for example, comprise a suitably programmed programmable controller or a hardware control circuit. One or more pressure sensors and/or flow sensors (not shown) may be included to provide feedback to the controller.
Any of cooling systems 100, 100A or 100B may be adapted for warming by replacing ice 66 with a suitable heating element which can be operated to warm fluid 65 in reservoir 64 to a desired temperature. Instead of ice 66, any of systems 100, 100A or 100B could include a refrigeration system to cool fluid 65.
Where a component (e.g. a member, assembly, element, device, circuit, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example:
